Class 2 (2nd Engineer) SC&S 📅 Nov 2022

Exam Question

(a) Describe how the force on the ship's bottom and the GM vary when grounding takes place. (6)

(b) The 1/2 ordinates of a waterplane at 15 m intervals, commencing from aft, are 1, 7, 10.5, 11, 11, 10.5, 8, 4 and 0 m. Calculate: (10)

(i) ТРC

(ii) Distance of the centre of flotation from midships

(iii) Second moment of area of the waterplane about a transverse axis through the centre of flotation.

Reference Answer

(a) When a ship grounds, the forces on the bottom and the metacentric height (GM) change depending on the grounding's nature and the ship's position on the seabed.
If the ship grounds on a level bottom:
A ground reaction force acts vertically upwards from the seabed. This force counteracts part of the ship's weight and alters the distribution of buoyancy forces.
The ship’s centre of gravity (G) may appear to rise relative to the metacentre (M) because the upward ground reaction reduces the buoyancy force acting on the underwater volume.

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